1. Field of the Invention
The present invention relates to the field of medical telemetry.
In particular, it relates to the field of medical telemetry wherein a medical device remotely collects an electric biological signal from a patient, processes the collected electric biological signal and transmits processed data to a centralized monitoring station over a radio communication network. From the centralized monitoring station, a technician or a doctor can monitor in real time the physiologic status of the patient.
For example, the electric biological signal may be an electric cardiac signal or an electric signal associated with activity of skeletal muscle.
The centralized monitoring station and/or the remote telemeter may support suitable diagnostic function for alerting the technician/doctor and/or the patient whenever a predetermined physiologic event occurs, such as a cardiac arrhythmia condition.
2. Description of the Related Art
US 2001/0023315 discloses a medical telemetry system for collecting real-time physiological data of patients of a medical facility, and of transferring the data via RF (Radio Frequency) to a real-time data distribution network for monitoring and display. The system includes battery-powered remote telemeters which attach to respective patients, and which collect and transmit (in data packet) the physiological data of the patients.
The remote telemeters communicate bi-directionally with a number of ceiling-mounted RF transceivers using a wireless TDMA (Time Division Multiple Access) protocol. The RF transceivers, which are hard-wire connected to a LAN, forward the data packets received from the telemeters to patient monitoring stations on the LAN.
JP 2002 219109 discloses a system wherein patient's ECG information is transmitted to an automatic diagnostic analyzer at a supervisory centre by cellular phone.
Paul A. Roche et al. (“Using a Cell Phone for Biotelemetry”, proceedings of the 2005 IEEE 31st Annual Northeast Bioengineering Conference, p. 65-66) discuss the benefits, obstacles, and methods of using cell phones to transmit biological waveforms to increase the mobility of patient monitoring. The Authors state that shielding the input cables will reduce the differential RF interference. Moreover, they state that the immunity of the sensitive electronics can be increased by inserting low-pass filters with maximum insertion loss at the cell phone's transmission frequency, reducing the RF seen at the inputs.
EP 1 589 464 discloses a diagnostic device comprising different sensors which can collect different electric biological signals such as heart rate, arterial pressure etc.; an analog-to-digital converter; a portable signal receiver which can analyze and process digitally converted data; and a transmission module to activate tele-transmission, via a telephone modem or GSM, to a central server. This document states that the analog-to-digital converter is placed close to the sensors so that the signals can be converted immediately on reception and transmitted digitally which is easier to manage and significantly reduces external interference.
As to the techniques disclosed by the above mentioned Paul A. Roche et al. to reduce interference problems, the Applicant notes that cable shielding can be insufficient. In particular, cable shielding can be inadequate to reduce interference occurring at the cable junctions (e.g., in the proximity of electrodes and connectors).
Moreover, as to the low-pass filtering technique disclosed by Paul A. Roche et al., the Applicant notes that such technique can be not adequate when an analog to digital (A/D) conversion of the collected biological waveform has to be performed for further data processing. In fact, in these cases, according to Shannon theorem, the collected biological waveform will be typically sampled at a sampling frequency that is at least twice the biological frequency range (which is usually below 200 Hz). Moreover, in order to improve performances, the biological waveform will be typically over-sampled at a sampling frequency that is at least three or four times the biological frequency range. Therefore, considering that medical devices with high accuracy and sensitivity may use a sampling frequency of 500 Hz, the cut-off frequency of the low-pass filter should be of at least 250 Hz. Therefore, a low-pass filter with cut-off frequency of not less of 250 Hz will be not adequate to filter out the GSM (Global System for Mobile communications) standard's demodulated frame rate of 217 Hz.